1. Field of the Invention
The present invention relates generally to radio communications equipment, and more particularly to an improved radio receiver squelch circuit having automatic means for setting the squelch level.
2. Description of the Prior Art
The use of squelch detection techniques for turning the audio section of communications receivers on and off in order to eliminate noise output from the audio section during periods when no signal is received is well known in the communications art. A common technique detects the base band noise which originates in the IF limiter or descriminator. In such squelch circuits, a potentiometer is often employed for setting the desired point at which the squelch operation is to occur. The potentiometer is manually controlled by the radio operator and must be adjusted to the desired squelch setting. To eliminate this inconvenience, some radios are equipped with squelch circuits that have preset controls. These controls are preset at a rather tight squelch in order to prevent an unsquelched condition due to circuit aging, noise level differences in various areas, and gain variations due to temperature. However, because of the insensitivity of this squelch control, messages transmitted with a low signal strength may be missed because of squelch insensitivity. There thus remains a need in the field for a reliable and inexpensive squelch circuit which will automatically adjust the squelch level and compensate for ambient noise and temperature variations.